Quantifying noise exposure and natural ventilation performance in urban areas

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Figure 6. Representation of example buildings used in the study. Building A and Building B are shown.
The main output used in these results from the EnergyPlus modelling was the energy consumption from a mixed mode cooling system. Mixed mode cooling is where the building’s internal comfort conditions are maintained by natural ventilation as much as possible, but then supplemented with varying amounts of mechanical cooling to maintain thermal comfort when needed. This strategy has been most widely used in offices. This approach was used here since pure natural ventilation would result in unacceptable levels of overheating, particularly when the ventilation openings are restricted due to noise.
The mixed mode cooling energy presented within the results can be taken as a proxy for natural ventilation performance. If the natural ventilation performance is successful then no or little mixed mode cooling energy is needed. If it is not successful, for example when the level of external noise means that natural ventilation openings are closed, then the mixed mode cooling use is high. This high use can be seen as tending towards a fully conditioned building.

  1. Results

The mixed mode cooling energy used for different tolerated noise levels, and therefore different ventilation opening patterns, for example building B, are shown in Figure 7. This indicates the type of output that this method can produce and more results can be found in the thesis by one of the authors3. Figure 8 shows the curve for building A with the effect of a 10 dB noise reduction measure estimated for location B. A 10dB noise reduction measure was chosen as an example as this is equivalent to a measure of medium effectiveness15. Assuming the noise reduction measure is applied uniformly for all ventilation openings then a lower level of mixed mode cooling energy is calculated for the same level of tolerated noise ingress (34 dBA). The 10 dB noise reduction measure equates to a 17 kW average chiller use for this case, resulting in an estimated 30% reduction in energy use.

Figure 7. Comparison of Building B in the different noise locations.
The differences in noise exposure between the two sites were quantified in the results by the separation of the curves. A greater tolerance of noise is needed in Location A for the same level of air conditioning used as in Location B. The distance between the curves for the buildings is related to the range of noise exposure for the two buildings in each location.

Figure 8. Illustration of how the change in chiller electricity due to a 10dB noise reduction measure is calculated for building A.

For the example buildings and locations investigated3 it was found that for the quieter noise location (site B) cooling requirements were found to decrease by 22%–45% compared to the noisier locations where natural ventilation was restricted. Site specific noise exposure patterns enabled the benefits of introducing noise reduction measures equal to 10 dB(A) to be quantified. This gave reductions in cooling energy consumption that varied from 28% to 45% of the original cooling energy consumption.

  1. Discussion

This integrated approach could be automated within building energy calculation tools if the required information was available. This would mean that this approach could fit into the building design process providing useful information. The change in cooling energy shown in these results demonstrated the importance of this integrated approach when deciding where to adopt natural and mixed mode ventilation strategies and whether noise mitigation methods are worth adopting in specific cases. The results show that the relationship between tolerated noise and chiller use follow a pattern that is represented schematically in Figure 9. Small changes in chiller use are seen when the ventilation openings tend toward fully closed or fully open. The main gains to be made from employing noise reduction measures to the ventilation opening are seen in the middle section of this graph. The details of a graph are specific to the building and its location so automation of the process would be key to its wider adoption.

Figure 9. Representation of usual relationship between noise and mixed mode chiller use.

  1. conclusion

This paper has given an overview of a method to integrate the noise and ventilation performance of buildings in urban buildings. The design curves that this method produced illustrate the essential relationship between noise and ventilation performance and illustrates how this method can inform the most effective use of noise reduction methods for specific sites.
  1. Acknowledgements

The authors would like to thank the Engineering and Physical Sciences Research Council (EPSRC) for their financial support of this work (grant ref. number EP/F038100/1) and also thank the China National Science Foundation CNSF (509288) for its contribution.

  1. References

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2. Oldham, D.J., De Salis, M.H.F., Sharples, S.: Reducing the ingress of urban noise through natural ventilation openings. Indoor Air. 14, 118–126 (2004).

3. Barclay, M.: PhD thesis - The interaction of building energy use, ventilation performance and urban noise under future climate scenarios, http://etheses.whiterose.ac.uk/4124/1/MB_Thesis_The_interaction_of_building_energy_use,_ventilation_performance_and_urban_noise_under_future_climate_scenarios.pdf, (2012).

4. Gomperts, M.C.: The “sound insulation” of circular and slit-shaped aperture. Acoustica. 14, 1–16 (1964).

5. Wilson, G.P.: Measurement of the Transmission Loss of a Finite-Depth Aperture. J. Acoust. Soc. Am. 37, 298–307 (1965).

6. Comsol Multiphysics: Acoustics Module, User’s Guide, (2008).

7. Oldham, D.J., Kang, J., Brocklesby, M.W.: Modelling the Acoustical and Airflow Performance of Simple Lined ventilation Apertures. Build. Acoust. 12, 277 – 292 (2005).

8. Wilson, G.P., Soroka, W.W.: Approximation to the Diffraction of Sound by a Circular Aperture in a Rigid Wall of Finite Thickness. J. Acoust. Soc. Am. 37, 286–297 (1965).

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10. DfT: Calculation of road traffic noise, (1988).

11. Mak, C., Leung, W., Jiang, G.: Measurement and prediction of road traffic noise at different building floor levels in Hong Kong. Build. Serv. Eng. Res. Technol. 31, 131–139 (2010).

12. Wang, B., Kang, J.: Effects of urban morphology on the traffic noise distribution through noise mapping: A comparative study between UK and China. Appl. Acoust. 72, 556–568 (2011).

13. Ordnance Survey: Roam Digimap image, http://edina.ac.uk/digimap/index.shtml, (2012).

14. Henninger, R.H., Witte, M.J.: EnergyPlus Testing with Building Thermal Envelope and Fabric Load Tests from ANSI/ASHRAE Standard 140-2007. U.S. Department of Energy, Office of Building Technologies Washington, D.C. (2009).

15. Kang, J., Brocklesby, M.W.: Feasibility of applying micro-perforated absorbers in acoustic window systems. Appl. Acoust. 66, 669–689 (2005).

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